NOx SENSOR DIAGNOSTIC FOR AN EXHAUST AFTERTREATMENT SYSTEM

ABSTRACT

A method for diagnosing NOx sensors in an exhaust aftertreatment system includes suspending reductant dosing in an exhaust aftertreatment system; purging a reductant deposit in a selective catalytic reduction (SCR) system of the exhaust aftertreatment system; adjusting at least one of an ignition timing and an engine speed for an engine to adjust an engine out nitrogen oxide (NOx) amount; receiving measured SCR inlet NOx data from a SCR inlet NOx sensor and measured SCR outlet NOx data from a SCR outlet NOx sensor; determining a phase shift between the measured SCR inlet and SCR outlet NOx data; applying the determined phase shift to the SCR outlet NOx data; and determining a diagnostic feature based on the SCR inlet NOx data and the phase shifted SCR outlet NOx data regarding a state of the SCR inlet and outlet NOx sensors.

BACKGROUND

Emissions regulations for internal combustion engines have become morestringent over recent years. Environmental concerns have motivated theimplementation of stricter emission requirements for internal combustionengines throughout much of the world. Governmental agencies, such as theEnvironmental Protection Agency (EPA) in the United States, carefullymonitor the emission quality of engines and set emission standards towhich engines must comply. Consequently, the use of exhaustaftertreatment systems on engines to reduce emissions is increasing.

Exhaust aftertreatment systems are generally designed to reduce emissionof particulate matter, nitrogen oxides (NOx), hydrocarbons, and otherenvironmentally harmful pollutants. However, the components that make upthe exhaust aftertreatment system can be susceptible to failure anddegradation. Because the failure or degradation of components may haveadverse consequences on performance and the emission-reductioncapability of the exhaust aftertreatment system, the detection and, ifpossible, correction of failed or degraded components is desirable. Infact, some regulations require on-board diagnostic (OBD) monitoring ortesting of many of the components of the exhaust aftertreatment system.When equipped on vehicles, most monitoring and testing of aftertreatmentsystem components are performed during on-road operation of the vehicle(e.g., while the vehicle is being driven on the road). Although suchmonitoring and testing may be convenient, the efficacy of the monitoringand testing may be limited because the engine cannot be operated outsideof a given on-road calibrated operating range. Additionally, becauseon-road operating demands typically have priority over diagnostic andperformance recovery procedures, the order, timing, and control of suchprocedures may be less than ideal. As a result, the detection andcorrection of various failure modes in the exhaust aftertreatment systemmay be limited.

SUMMARY

One embodiment relates to an apparatus including a dosing module, anengine module, a selective catalytic reduction (SCR) inlet NOx module, aSCR outlet NOx module, a phase correction module, and a systemdiagnostic module. The dosing module is structured to suspend dosing inan exhaust aftertreatment system. The engine module is structured toprovide a command to an engine to affect an engine out nitrogen oxide(NOx) amount. The SCR inlet NOx module is structured to interpretmeasured SCR inlet NOx data from a SCR inlet NOx sensor. The SCR outletNOx module is structured to interpret measured SCR outlet NOx data froma SCR outlet NOx sensor. The phase correction module is structured todetermine a phase shift between the measured SCR inlet NOx data and themeasured SCR outlet NOx data and apply the phase shift to the measuredSCR outlet NOx amount data. The system diagnostic module is structuredto determine a diagnostic feature based on the SCR inlet NOx data andthe phase shifted SCR outlet NOx data, wherein the system diagnosticmodule is structured to determine a state of the SCR inlet and outletNOx sensors based on the diagnostic feature, the state including atleast one of an operational state and at least one of the SCR inlet andoutlet NOx sensor are faulty. The apparatus provides a servicetechnician the ability to diagnose exhaust aftertreatment problems tothe SCR inlet and outlet NOx sensors, which thereby alleviates the needfor costly and timely service diagnostics regarding the whole exhaustaftertreatment system.

Another embodiment relates to a method for diagnosing NOx sensors in anexhaust aftertreatment system. The method includes suspending reductantdosing in an exhaust aftertreatment system; purging a reductant depositin a selective catalytic reduction (SCR) system of the exhaustaftertreatment system; adjusting at least one of an ignition timing andan engine speed for an engine to adjust an engine out nitrogen oxide(NOx) amount; interpreting measured SCR inlet NOx data from a SCR inletNOx sensor and measured SCR outlet NOx data from a SCR outlet NOxsensor; determining a phase shift between the measured SCR inlet and SCRoutlet NOx data; applying the determined phase shift to the SCR outletNOx data; and determining a diagnostic feature based on the SCR inletNOx data and the phase shifted SCR outlet NOx data regarding a state ofthe SCR inlet and outlet NOx sensors. According to one embodiment, themethod is performed as an intrusive diagnostic tool for an engine andexhaust aftertreatment system, wherein the method controls operation ofthe engine and exhaust aftertreatment system.

Another embodiment relates to a system including an engine; an exhaustaftertreatment system in exhaust gas receiving communication with theengine, wherein the exhaust aftertreatment system includes a selectivecatalytic reduction (SCR) system; and a controller communicably coupledto the engine and the exhaust aftertreatment system. The controller isstructured to suspend reductant dosing in the exhaust aftertreatmentsystem; purge a reductant deposit in the SCR system; adjust a nitrogenoxide (NOx) amount out of the engine that is then received by the SCRsystem; interpret measured SCR inlet NOx data from a SCR inlet NOxsensor and measured SCR outlet NOx data from a SCR outlet NOx sensor;determine a phase shift between the measured SCR inlet and SCR outletNOx data; apply the determined phase shift to the SCR outlet NOx data;and determine a diagnostic feature based on the SCR inlet NOx data andthe phase shifted SCR outlet NOx data regarding a state of the SCR inletand outlet NOx sensors. By utilizing measured SCR inlet and outlet NOxdata, the controller is able to relatively more accurately diagnose theSCR inlet and outlet NOx sensors for the aftertreatment system.

These and other features, together with the organization and manner ofoperation thereof, will become apparent from the following detaileddescription when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an exhaust aftertreatment system with acontroller, according to an example embodiment.

FIG. 2 is a schematic diagram of the controller used with the system ofFIG. 1, according to an example embodiment.

FIG. 3 is a flow diagram of a method of performing a NOx sensordiagnostic for an exhaust aftertreatment system, according to an exampleembodiment.

FIG. 4 are graphs corresponding to a selective catalytic reduction (SCR)system diagnostic test, according to an example embodiment.

FIG. 5 is a graph depicting SCR NOx inlet and outlet data as a functionof ignition timing and engine speed, according to an example embodiment.

FIG. 6 is a graph of outlet NOx sensor data versus inlet NOx sensor datashowing the effect of transport delay, according to an exampleembodiment.

FIG. 7 is a graph of a cross-correlation function of outlet NOx sensordata and inlet NOx sensor data, according to an example embodiment.

FIG. 8 is a graph of outlet NOx sensor data versus inlet NOx sensor datawith a time shift correction, according to an example embodiment.

FIG. 9 are a series of graphs depicting various failure modes for SCRNOx inlet and NOx outlet sensors, according to an example embodiment.

FIG. 10 is a graph of outlet NOx sensor data versus inlet NOx sensordata with a failed NOx outlet sensor, according to an exampleembodiment.

FIG. 11 is a graph of outlet NOx sensor data versus inlet NOx sensordata with reductant deposits present in the aftertreatment systembetween the inlet NOx and outlet NOx sensors, according to an exampleembodiment.

FIG. 12 is a graph of a NOx conversion fraction between outlet NOxsensor data and inlet NOx sensor data with reductant deposits present inthe aftertreatment system, according to an example embodiment.

DETAILED DESCRIPTION

Referring to the Figures generally, the various embodiments disclosedherein relate to a system and method of diagnosing NOx sensors in anexhaust aftertreatment system. According to the present disclosure, acontroller performs an intrusive diagnostic procedure that manipulates aNOx amount out of an engine, measures the resulting NOx amount across aselective catalytic reduction (SCR) system, and determines whether(among other failure modes) the NOx inlet and NOx outlet sensor arefaulty by utilizing one or more diagnostic features, which are describedmore fully herein. As a brief overview, some engine systems includeexhaust aftertreatment systems for decreasing the pollutants emittedfrom the engine systems. Among other components, these exhaustaftertreatment systems may include a SCR system. The SCR includes a SCRcatalyst that is designed to reduce the nitrous oxides (NOx) in engineexhaust gas to nitrogen and other less pollutant compounds. Toaccomplish this reduction, a reductant is sprayed into the exhaust gasstream prior to the exhaust gas reaching the SCR system. Over the SCRcatalyst, the NOx reacts with ammonia that formed from the decompositionof the reductant, to form nitrogen and other less harmful compounds. Inturn, a decrease in NOx emissions from the exhaust gas is accomplished.The efficiency of the SCR catalyst may be determined by measuring thereduction of NOx emissions from the exhaust gas between the inlet to theoutlet of the SCR catalyst, which is described more fully below.

In certain embodiments, SCR efficiency may be determined by a NOxconversion fraction for the exhaust gas. The NOx conversion fraction maybe determined from NOx data regarding the exhaust gas stream from theengine. For example, the NOx data may include an SCR inlet NOx amount(represented as NOx, inlet in equation [1] below). The NOx data may alsoinclude an SCR outlet NOx amount (represented as NOx, outlet in equation[1] below). Taking a difference between these two amounts, the NOxconversion fraction represents the percent reduction in NOx in theexhaust gas stream accomplished by the SCR system. According to oneembodiment, the NOx conversion fraction amount may be determined asfollows:

[(NOx,inlet−NOx,outlet)/NOx,inlet]×100=NOx conversion fractionpercent  [1]

The NOx conversion fraction provides an indication of the efficacy ofthe SCR system. For example, a relatively higher conversion fractionindicates that a substantial amount of the NOx present in the exhauststream is being reduced to nitrogen and other less pollutant compounds.However, a relatively lower conversion fraction indicates that the NOxin the exhaust gas stream is substantially not being converted tonitrogen and other less pollutant compounds.

In any event, the NOx conversion fraction may not be the only indicatorof SCR efficiency. Low observed SCR efficiency may be caused by severalcomponents and interactions in the aftertreatment system. Componentfailures and interactions may make it difficult to correctly isolate thesource of the malfunction. There are several scenarios where falsefaults (e.g., the SCR catalyst is functioning properly but a low SCRefficiency is observed) are possible (e.g., due to sensor failures,etc.). The numerous component failures which may cause a low SCRefficiency include, but are not limited to, the following failedcomponents: the SCR inlet NOx sensor, the SCR outlet NOx sensor, thediesel exhaust fluid (DEF) dosing system, the diesel oxidation catalyst(DOC)/diesel particulate filter (DPF) unit, and the SCR/Ammoniaoxidation (AMOx) catalyst unit.

According to the present disclosure, a controller isolates the lowobserved SCR efficiency to the SCR inlet and outlet NOx sensors if theyare in fact faulty. Because these are typically the lowest cost items inthe aftertreatment system, successful identification of them beingfaulty may save costs by removing the need to service/troubleshoot otheraftertreatment components. However, the technician may still need toperform other troubleshooting if the controller determines that the NOxsensors are operational. With that in mind, according to the presentdisclosure, a controller provides one or more dosing commands to suspendthe reductant dosing in the aftertreatment system. Following the dosingsuspension, the residual reductant deposits within the SCR catalyst maybe purged via thermal decomposition. By suspending dosing and purgingthe reductant, the NOx amount entering and leaving the SCR catalyst mayremain relatively constant. The controller then provides one or moreengine operation commands to adjust an engine out NOx amount. The NOxamount entering and leaving the SCR system is then measured by SCR inletand outlet NOx sensors. The controller uses the measured SCR inlet andoutlet NOx data to determine one or more diagnostic features (e.g., again associated with the data). Based on the one or more diagnosticfeatures determined from the measured data, the state of the NOx sensors(e.g., faulty or operational) may be determined. Based on the statedetermined, the controller may provide one or more notifications (e.g.,a fault code) to a user of the exhaust aftertreatment system indicatingwhether service, repair, maintenance, and the like of the NOx inlet andoutlet sensor is needed. Accordingly, the system and method describedherein enable the diagnosis of SCR NOx sensors by exciting the NOxsignals from adjusting the engine out NOx amount and accounting for thedynamics between the inlet and outlet NOx sensor signals. Conventionaldiagnostic systems do not utilize and, therefore, do not appreciate thebetter diagnostic data received from exciting the NOx signals todiagnose NOx sensors as in the present disclosure. Exciting the NOxamount signals leads to richer NOx signals that yield a more accurate,more efficient diagnostic procedure. As such, the present disclosureprovides for a technical improvement over conventional systems thatresults in a more accurate diagnostic procedure utilizing a moreefficient use of resources (i.e., the system and method described hereintend to correctly identify whether the NOx sensors are faulty withoutthe need for further troubleshooting thereby saving time and money).Further, by correctly identifying faults in the exhaust aftertreatmentsystem that are caused by faulty SCR NOx sensors, timely and costlyservice trips may be avoided as the SCR NOx sensors are substantiallyless costly relative to other components.

As used herein, the term “intrusive” (in regard to performing one ormore diagnostic tests) is used to refer to an active diagnostic test. Inother words, the intrusive method, system, and apparatus describe adiagnostic test or protocol that is forced to run on the engine andexhaust aftertreatment system (i.e., causes the engine to operate at acertain speed, etc.). As a result, the active or intrusive diagnostictest is often run in a service bay or test center environment. Incomparison, a passive diagnostic test may be performed while the engineand exhaust aftertreatment system are operational. For example, ifembodied in a vehicle, the passive test may be performed while theoperator is driving the vehicle. If an error is detected, a fault codeor indicator lamp may be actuated to alert the operator ofmaintenance/service that may be required. According to the presentdisclosure, an intrusive method, system, and apparatus is utilized withthe engine and exhaust aftertreatment system to manipulate or excite theNOx emissions in the exhaust gas stream from the engine system. In thisregard, the “intrusive diagnostic test” of the present disclosure mayinclude overriding various set engine operating points to perform thediagnostic test. For example, many engine operating points are set to bein compliance with one or more vehicular laws (e.g., emissions). Byoverriding one or more of these operating points, the engine may beforced into non-compliance with one or more vehicular laws. However,this intrusive test, procedure, and/or protocol allows for the effectivediagnosis of a SCR inlet NOx sensor and a SCR outlet NOx sensor of theexhaust aftertreatment system to determine whether the sensors need tobe repaired, replaced, or otherwise serviced.

Referring now to FIG. 1, an engine exhaust aftertreatment system with acontroller is shown, according to an example embodiment. The enginesystem 10 includes an internal combustion engine 20 and an exhaustaftertreatment system 22 in exhaust gas-receiving communication with theengine 20. According to one embodiment, the engine 20 is structured as acompression-ignition internal combustion engine that utilizes dieselfuel. However, in various alternate embodiments, the engine 20 may bestructured as any other type of engine (e.g., spark-ignition) thatutilizes any type of fuel (e.g., gasoline). Within the internalcombustion engine 20, air from the atmosphere is combined with fuel, andcombusted, to power the engine. Combustion of the fuel and air in thecompression chambers of the engine 20 produces exhaust gas that isoperatively vented to an exhaust manifold and to the exhaustaftertreatment system 22.

In the example depicted, the exhaust aftertreatment system 22 includes adiesel particular filter (DPF) 40, a diesel oxidation catalyst (DOC) 30,a selective catalytic reduction (SCR) system 52 with a SCR catalyst 50,and an ammonia oxidation (AMOx) catalyst 60. The SCR system 52 furtherincludes a reductant delivery system that has a diesel exhaust fluid(DEF) source 54 that supplies DEF to a DEF doser 56 via a DEF line 58.

In an exhaust flow direction, as indicated by directional arrow 29,exhaust gas flows from the engine 20 into inlet piping 24 of the exhaustaftertreatment system 22. From the inlet piping 24, the exhaust gasflows into the DOC 30 and exits the DOC into a first section of exhaustpiping 28A. From the first section of exhaust piping 28A, the exhaustgas flows into the DPF 40 and exits the DPF into a second section ofexhaust piping 28B. From the second section of exhaust piping 28B, theexhaust gas flows into the SCR catalyst 50 and exits the SCR catalystinto the third section of exhaust piping 28C. As the exhaust gas flowsthrough the second section of exhaust piping 28B, it is periodicallydosed with DEF by the DEF doser 56. Accordingly, the second section ofexhaust piping 28B acts as a decomposition chamber or tube to facilitatethe decomposition of the DEF to ammonia. From the third section ofexhaust piping 28C, the exhaust gas flows into the AMOx catalyst 60 andexits the AMOx catalyst into outlet piping 26 before the exhaust gas isexpelled from the exhaust aftertreatment system 22. Based on theforegoing, in the illustrated embodiment, the DOC 30 is positionedupstream of the DPF 40 and the SCR catalyst 50, and the SCR catalyst 50is positioned downstream of the DPF 40 and upstream of the AMOX catalyst60. However, in alternative embodiments, other arrangements of thecomponents of the exhaust aftertreatment system 22 are also possible

The DOC 30 may have any of various flow-through designs. Generally, theDOC 30 is structured to oxidize at least some particulate matter, e.g.,the soluble organic fraction of soot, in the exhaust and reduce unburnedhydrocarbons and CO in the exhaust to less environmentally harmfulcompounds. For example, the DOC 30 may be structured to reduce thehydrocarbon and CO concentrations in the exhaust to meet the requisiteemissions standards for those components of the exhaust gas. An indirectconsequence of the oxidation capabilities of the DOC 30 is the abilityof the DOC to oxidize NO into NO₂. In this manner, the level of NO₂exiting the DOC 30 is equal to the NO₂ in the exhaust gas generated bythe engine 20 plus the NO₂ converted from NO by the DOC.

In addition to treating the hydrocarbon and CO concentrations in theexhaust gas, the DOC 30 may also be used in the controlled regenerationof the DPF 40, SCR catalyst 50, and AMOx catalyst 60. This can beaccomplished through the injection, or dosing, of unburned HC into theexhaust gas upstream of the DOC 30. Upon contact with the DOC 30, theunburned HC undergoes an exothermic oxidation reaction which leads to anincrease in the temperature of the exhaust gas exiting the DOC 30 andsubsequently entering the DPF 40, SCR catalyst 50, and/or the AMOxcatalyst 60. The amount of unburned HC added to the exhaust gas isselected to achieve the desired temperature increase or targetcontrolled regeneration temperature.

The DPF 40 may be any of various flow-through or wall-flow designs, andis structured to reduce particulate matter concentrations, e.g., sootand ash, in the exhaust gas to meet or substantially meet requisiteemission standards. The DPF 40 captures particulate matter and otherconstituents, and thus may need to be periodically regenerated to burnoff the captured constituents. Additionally, the DPF 40 may beconfigured to oxidize NO to form NO₂ independent of the DOC 30.

As discussed above, the SCR system 52 may include a reductant deliverysystem with a reductant (e.g., DEF) source 54, a pump and a deliverymechanism or doser 56. The reductant source 54 can be a container ortank capable of retaining a reductant, such as, for example, ammonia(NH₃), DEF (e.g., urea), or diesel oil. The reductant source 54 is inreductant supplying communication with the pump, which is configured topump reductant from the reductant source to the delivery mechanism 56via a reductant delivery line 58. The delivery mechanism 56 ispositioned upstream of the SCR catalyst 50. The delivery mechanism 56 isselectively controllable to inject reductant directly into the exhaustgas stream prior to entering the SCR catalyst 50. As described herein,the controller 100 is structured to control the timing and amount of thereductant delivered to the exhaust gas. In some embodiments, thereductant may either be ammonia or DEF, which decomposes to produceammonia. As briefly described above, the ammonia reacts with NOx in thepresence of the SCR catalyst 50 to reduce the NOx to less harmfulemissions, such as N₂ and H₂O. The NOx in the exhaust gas streamincludes NO₂ and NO. Generally, both NO₂ and NO are reduced to N₂ andH₂O through various chemical reactions driven by the catalytic elementsof the SCR catalyst in the presence of NH₃.

The SCR catalyst 50 may be any of various catalysts known in the art.For example, in some implementations, the SCR catalyst 50 is avanadium-based catalyst, and in other implementations, the SCR catalystis a zeolite-based catalyst, such as a Cu-Zeolite or a Fe-Zeolitecatalyst.

The AMOx catalyst 60 may be any of various flow-through catalystsconfigured to react with ammonia to produce mainly nitrogen. As brieflydescribed above, the AMOx catalyst 60 is structured to remove ammoniathat has slipped through or exited the SCR catalyst 50 without reactingwith NOx in the exhaust. In certain instances, the exhaustaftertreatment system 22 may be operable with or without an AMOxcatalyst. Further, although the AMOx catalyst 60 is shown as a separateunit from the SCR catalyst 50 in FIG. 1, in some implementations, theAMOx catalyst may be integrated with the SCR catalyst, e.g., the AMOxcatalyst and the SCR catalyst can be located within the same housing.According to the present disclosure, the SCR catalyst and AMOx catalystare positioned serially, with the SCR catalyst preceding the AMOxcatalyst. As described above, in various other embodiments, the AMOxcatalyst is not included in the exhaust aftertreatment system 22. Inthese embodiments, the NOx sensor 14 may be excluded from the exhaustaftertreatment system 22 as well.

Various sensors, such as NH₃ sensor 72, NOx sensors 12, 14, 55, 57 andtemperature sensors 16, 18, may be strategically disposed throughout theexhaust aftertreatment system 22 and may be in communication with thecontroller 100 to monitor operating conditions of the engine system 10.As shown, more than one NOx sensor may be positioned upstream anddownstream of the SCR catalyst 50. In this configuration, the NOx sensor12 measures the engine out NOx while the NOx sensor 55 measures the SCRcatalyst 50 inlet NOx amount, which is referred to as the SCR inlet NOxsensor 55 herein. Due to the DOC 30/DPF 40 potentially oxidizing someportion of the engine out NOx (e.g., NO, etc.), the proportions ofengine out NOx amount (e.g, NO, NO₂, etc.) may not be equal to theproportions of SCR catalyst 50 inlet NOx amount. For example, while NOmay be oxidized to NO₂ in the DOC 30/DPF 40 such that the relativeproportions of NO, NO₂, etc. may not be equal to the originalproportions from the engine, the total concentration of NOx remains thesame. The NOx sensors 12, 14, 55, 57 tend to have a lower sensitivity toNO₂ which causes the sensed NOx amount to change with the ratio ofNO₂/NOx. Accordingly, this configuration accounts for this potentialdiscrepancy. The NOx amount leaving the SCR catalyst 50 may be measuredby the NOx sensor 57 and/or the NOx sensor 14. In some embodiments,there may be only NOx sensor 57 or NOx sensor 14 depending on whetherthe configuration of the exhaust aftertreatment system 22 includes theAMOx catalyst 60. The NOx sensor 57 is positioned downstream of the SCRcatalyst 50 and is structured to detect the concentration of NOx in theexhaust gas downstream of the SCR catalyst 50 (e.g., exiting the SCRcatalyst), which is referred to as the SCR outlet NOx sensor 57 herein.

The temperature sensors 16 are associated with the DOC 30 and DPF 40,and thus can be defined as the DOC/DPF temperature sensors 16. TheDOC/DPF temperature sensors are strategically positioned to detect thetemperature of exhaust gas flowing into the DOC 30, out of the DOC andinto the DPF 40, and out of the DPF before being dosed with DEF by thedoser 56. The temperature sensors 18 are associated with the SCRcatalyst 50 and AMOx catalyst 60 and thus can be defined as SCR/AMOxtemperature sensors 18. The SCR/AMOx temperature sensors 18 arestrategically positioned to detect the temperature of exhaust gasflowing into the SCR catalyst 50, out of the SCR catalyst 50, into theAMOx catalyst 60, and out of the AMOx catalyst 60. By way of example,temperature sensors may be strategically positioned before and after anycomponent within the exhaust aftertreatment system 22 such that thetemperature of the exhaust gas flowing into and out of any component maybe detected and communicably transmitted to the controller 100.

As shown in FIG. 1, a particulate matter (PM) sensor 70 is positioneddownstream of the SCR 50. According to one embodiment, the PM sensor 70is positioned in any position downstream of the DPF 40. Accordingly,other locations of the PM sensor 70 are also depicted in FIG. 1: afterthe DPF 40, after the AMOx catalyst 60, after the SCR catalyst 50, etc.In some embodiments, more than one PM sensor 70, as shown in FIG. 1, mayalso be included in the system. The PM sensor 70 is structured tomonitor particulate matter flowing through the exhaust aftertreatmentsystem 22. By monitoring the particulate matter, the PM sensor 70monitors the functionality of the DPF 40 and/or other components of theexhaust aftertreatment system 22.

Although the exhaust aftertreatment system 22 shown includes one of aDOC 30, DPF 40, SCR catalyst 50, and AMOx catalyst 60 positioned inspecific locations relative to each other along the exhaust flow path,in other embodiments, the exhaust aftertreatment system may include morethan one of any of the various catalysts positioned in any of variouspositions relative to each other along the exhaust flow path as desired.Further, although the DOC 30 and AMOX catalyst 60 are non-selectivecatalysts, in some embodiments, the DOC and AMOX catalyst can beselective catalysts.

FIG. 1 is also shown to include an operator input/output (I/O) device120. The operator I/O device 120 is communicably coupled to thecontroller 100, such that information may be exchanged between thecontroller 100 and the I/O device 120, wherein the information mayrelate to one or more components of FIG. 1 or determinations (describedbelow) of the controller 100. The operator I/O device 120 enables anoperator of the engine system 10 to communicate with the controller 100and one or more components of the engine system 10 of FIG. 1. Forexample, the operator input/output device 120 may include, but is notlimited to, an interactive display, a touchscreen device, one or morebuttons and switches, voice command receivers, etc. In various alternateembodiments, the controller 100 and components described herein may beimplemented with non-vehicular applications (e.g., a power generator).Accordingly, the I/O device may be specific to those applications. Forexample, in those instances, the I/O device may include a laptopcomputer, a tablet computer, a desktop computer, a phone, a watch, apersonal digital assistant, etc. Via the I/O device 120, the controller100 may provide a fault or service notification based on the determinedstate of the SCR catalysts 50 and the SCR inlet and outlet NOx sensors55 and 57 (in some embodiments, when the AMOx catalyst is included, theNOx sensor 14).

The controller 100 is structured to control the operation of the enginesystem 10 and associated sub-systems, such as the internal combustionengine 20 and the exhaust gas aftertreatment system 22. According to oneembodiment, the components of FIG. 1 are embodied in a vehicle. Invarious alternate embodiments, as described above, the controller 100may be used with any engine-exhaust aftertreatment system. The vehiclemay include an on-road or an off-road vehicle including, but not limitedto, line-haul trucks, mid-range trucks (e.g., pick-up trucks), tanks,airplanes, and any other type of vehicle that utilizes an exhaustaftertreatment system. Communication between and among the componentsmay be via any number of wired or wireless connections. For example, awired connection may include a serial cable, a fiber optic cable, a CAT5cable, or any other form of wired connection. In comparison, a wirelessconnection may include the Internet, Wi-Fi, cellular, radio, etc. In oneembodiment, a controller area network (CAN) bus provides the exchange ofsignals, information, and/or data. The CAN bus includes any number ofwired and wireless connections. Because the controller 100 iscommunicably coupled to the systems and components of FIG. 1, thecontroller 100 is structured to receive data from one or more of thecomponents shown in FIG. 1. For example, the data may include NOx data(e.g., an incoming NOx amount from SCR inlet NOx sensor 55 and anoutgoing NOx amount from SCR outlet NOx sensor 57), dosing data (e.g.,timing and amount of dosing delivered from doser 56), and vehicleoperating data (e.g., engine speed, vehicle speed, engine temperature,etc.) received via one or more sensors. As another example, the data mayinclude an input from operator input/output device 120. The structureand function of the controller 100 is further described in regard toFIG. 2.

As such, referring now to FIG. 2, an example structure for thecontroller 100 is shown according to one embodiment. As shown, thecontroller 100 includes a processing circuit 101 including a processor102 and a memory 103. The processor 102 may be implemented as ageneral-purpose processor, an application specific integrated circuit(ASIC), one or more field programmable gate arrays (FPGAs), a digitalsignal processor (DSP), a group of processing components, or othersuitable electronic processing components. The one or more memorydevices 103 (e.g., RAM, ROM, Flash Memory, hard disk storage, etc.) maystore data and/or computer code for facilitating the various processesdescribed herein. Thus, the one or more memory devices 103 may becommunicably connected to the processor 102 and provide computer code orinstructions to the processor 102 for executing the processes describedin regard to the controller 100 herein. Moreover, the one or more memorydevices 103 may be or include tangible, non-transient volatile memory ornon-volatile memory. Accordingly, the one or more memory devices 103 mayinclude database components, object code components, script components,or any other type of information structure for supporting the variousactivities and information structures described herein.

The memory 103 is shown to include various modules for completing theactivities described herein. More particularly, the memory 103 includesmodules structured to diagnose the SCR inlet and outlet NOx sensors 55and 57 (in some embodiments, the diagnosis may include NOx sensor 14).While various modules with particular functionality are shown in FIG. 2,it should be understood that the controller 100 and memory 103 mayinclude any number of modules for completing the functions describedherein. For example, the activities of multiple modules may be combinedas a single module, additional modules with additional functionality maybe included, etc. Further, it should be understood that the controller100 may further control other vehicle activity beyond the scope of thepresent disclosure.

Certain operations of the controller 100 described herein includeoperations to interpret and/or to determine one or more parameters.Interpreting or determining, as utilized herein, includes receivingvalues by any method known in the art, including at least receivingvalues from a datalink or network communication, receiving an electronicsignal (e.g. a voltage, frequency, current, or PWM signal) indicative ofthe value, receiving a computer generated parameter indicative of thevalue, reading the value from a memory location on a non-transientcomputer readable storage medium, receiving the value as a run-timeparameter by any means known in the art, and/or by receiving a value bywhich the interpreted parameter can be calculated, and/or by referencinga default value that is interpreted to be the parameter value.

As shown, the controller 100 includes a dosing module 104, an enginemodule 105, a SCR inlet NOx module 106, a SCR outlet NOx module 107, aphase correction module 108, a system diagnostic module 109, and anotification module 110. The dosing module 104 is structured to providea dosing command to a reductant doser, such as doser 56. The dosingcommand may include at least one of a command to suspend reductantdosing injection into the exhaust flow and a command to increase,decrease, or maintain a reductant dosing injection into the exhaustflow. Reductant dosing decreases the levels of NOx in the exhaust gaswhich causes the SCR outlet NOx sensor 57 to measure lower amounts ofNOx than the SCR inlet NOx sensor 55. Therefore, by suspending thereductant dosing, the SCR NOx sensors should theoretically measureapproximately the same levels of NOx in the exhaust flow if each sensoris functioning properly. However, there still may be trace amounts ofreductant (e.g., ammonia) present in the SCR system that cause oxidationof the NOx in the exhaust gas flow such that the measurements from theSCR inlet and outlet sensors may not be exactly equal. As described morefully herein, to diagnose at least one of the SCR inlet NOx sensor andthe SCR outlet NOx sensor, the dosing module 104 is structured to firstsuspend dosing.

The engine module 105 is structured to provide an engine operationcommand to the engine 20. The engine operation command is structured topurge the residual reductant in the SCR system 52. The engine operationcommand is also structured to adjust or perturb a NOx amount out of theengine. The engine operation command may include, but is not limited to,an ignition timing adjustment, an engine speed adjustment, an exhaustgas recirculation (EGR) flow amount adjustment, fuel injection timingadjustment, fuel injection pressure adjustment, a fuel injection amountadjustment, an air flow amount, a number of fuel injection pulses, afuel flow amount, and an engine torque output, among other alternatives.The engine operation commands may be provided individually or with othercommands. The extent to which any of the foregoing engine operationcommands may be used and in what combination may vary based on enginedesign and/or engine application.

As mentioned above, the engine operation command may be structured toadjust or affect an engine out NOx amount. To adjust the engine out NOxamount, the engine module 105 may command an adjustment to at least oneof the ignition timing, the engine speed, the EGR flow, the fuelinjection timing, the fuel injection pressure, the number of fuelinjection pulses, the fuel flow amount, and the engine torque amount.The ignition timing adjustment command may include at least one of anadvance to ignition timing and a retarding to ignition timing. In acompression-ignition engine, ignition timing adjustment refers to whenfuel is injected into a combustion chamber. In comparison, ignitiontiming adjustment in a spark-ignition engine refers to when a spark iscommanded. Thus, when the controller 100 is embodied with acompression-ignition engine, the engine module 105 may provide a commandto a fuel injector (including a solenoid or other fuel injector driverand the components related to the fuel injector, such as a common rail)to adjust when fuel is injected into the combustion chamber. When thecontroller 100 is embodied in a spark-ignition engine, the engine module105 may provide a command to a spark plug or igniter (including anyspark plug or igniter drivers, such as a solenoid or a transformer for apower supply) to adjust when the spark event is initiated. Accordingly,while the description below is substantially in regard tocompression-ignition engines (e.g., fuel injectors), it should beunderstood that similar commands may be provided with spark-ignitioncommands such that all such variations fall within the spirit and scopeof the present disclosure.

Therefore, as mentioned above, the engine module 105 may provide anignition timing adjustment command that includes at least one ofretarding and advancing ignition timing. The timing may be adjusted toincrease or decrease the NOx production of the engine 20. Advancing theignition timing refers to commanding fuel injection relatively earlierthan it otherwise would occur. In comparison, retarding ignition timingrefers to delaying a fuel injection event. For example, if the ignitiontiming of an engine is set to nine degrees before top dead center (BTDC)and is adjusted to twelve degrees BTDC, the ignition timing is advanced.Proper ignition timing may be critical for optimum performance, fueleconomy, and emissions. Advancing ignition timing may result inincreases to both the temperature and pressure within the enginecylinders. Because NOx formation tends to occur at relatively highercombustion temperatures, the NOx amount out of the engine may increasedue to this command. In comparison, retarding ignition timing may resultin lower temperature and pressures within the combustion cylinder. As aresult, a relatively smaller amount of NOx out of the engine may occur.Thus, the engine module 105 may provide one or more commands to adjustthe ignition timing, which results in a change in a NOx amount out ofthe engine and excites the measurements of the SCR inlet and outlet NOxsensors 55 and 57.

As mentioned above, the engine operation command from the engine module105 may also include an adjustment to engine speed (i.e.,revolutions-per-minute (RPM)). By increasing the engine speed, theaverage temperature of the engine cylinders may rise as heat is spreadrelatively more rapidly throughout the combustion chamber. Over time,the average temperature in the cylinder rises. This is due to thepresence of relatively fewer lower temperature areas that wouldotherwise cause the temperature to descend. Therefore, because NOxproduction is highly dependent on high temperature, by increasing enginespeed, the engine out NOx amount exhaust may increase. On the otherhand, decreasing engine speed may have the opposite effect. This is dueto a relatively greater number of low temperature areas in and aroundthe combustion chamber that in essence ‘cool’ the combustion gases. Assuch, the temperature may decrease and in turn, the engine out amount ofNOx may decrease. Increasing the engine speed demands a significantincrease to the indicated torque and fuel flow to the engine 20, whichmay increase NOx production. Further, the increased flow through theengine provides a wider operating space to adjust the engine operationcommands, allowing the possibility for finding a combination of engineoperation commands that provides a higher NOx concentration than ispossible at a lower speed.

The engine operation command from the engine module 105 may also includean adjustment to EGR flow. EGR is an emission control technologyallowing substantial decreases in NOx emissions when the EGR flow isincreased, and substantial increases when the EGR flow is decreased orstopped. Essentially, the amount of NOx decreases as the EGR rateincreases. Also, NOx reduction at a given EGR rate increases as theengine load becomes higher. For example, a given decrease in NOxemissions may require less EGR at high loads (e.g., high engine torque,etc.) than at low loads (e.g., low engine torque, etc.). The engineoperation command from the engine module 105 may adjust injectionpressure. An increase in the fuel injection pressure may result in anincrease in the NOx emissions at medium and at high engine loads (e.g.,mid-to-high engine torque, etc.), while a decrease in the fuel injectionpressure may decrease the NOx emissions. Multi-pulse injection may beused to lengthen the combustion event, thus increasing the amount ofheat is the system, thereby facilitating the generation of greateramounts of NOx emissions. In some embodiments, engine brakes may be usedto increase the load on the engine 20 or a variable geometryturbocharger (VGT) may also be used to increase load and flow bybuilding exhaust backpressure. As described above, greater engine loadmay increase the NOx emissions. It should be noted that any of theforegoing engine operation commands may be used individually or incombination. As such, multiple engine commands may be usedsimultaneously to affect an increase or decrease in the NOx emissions ofthe engine 20.

Thus, the engine module 105 may provide one or more commands (e.g.,advancing ignition timing and increasing engine speed, etc.) that arestructured to excite (e.g., increase or decrease) an engine out NOxamount. While the embodiments described and disclosed herein areprimarily in regard to increasing the engine out NOx amount to performthe diagnostic test, it should be understood that similar processes asthose described herein may be utilized with commanded decreasing amountsof engine out NOx. All such variations are intended to be within thespirit and scope of the present disclosure.

Furthermore, as mentioned above, after the dosing module 104 suspendsdosing, the engine module 105 is also structured to substantially purgethe reductant deposits remaining in the SCR system 52. By removing(i.e., purging) the reductant from the system, the NOx in the exhaustgas flowing through the SCR system is substantially prevented fromreducing via the reductant as the exhaust gas flows across the SCRcatalyst 50. This may allow the SCR inlet and outlet NOx sensors 55 and57 to substantially measure the same gas composition (i.e., NOx amount)during the diagnostic test. The purging of the reductant deposits may bedone either mechanically or thermally. Thermal purging may be caused byan engine command from the engine module 105 that is structured toincrease the temperature of the exhaust gas and burn off reductantdeposits in the SCR system. As mentioned above, the engine module 105may provide a command to at least one of increase engine speed andadvance ignition timing. In other embodiments, the engine module 105 mayuse any command that raises the exhaust gas temperature to burn off orpurge reductant deposits in the SCR system 52. For example, the enginemodule 105 may command a post-combustion fuel injection. The added fuelcreates additional heat as it is transported with the exhaust gas to theDOC. As a result, the exhaust gas temperatures increase. By providingthese commands, the temperature of exhaust gas within the exhaustaftertreatment system 22 may be substantially increased. With theincrease in the temperature, the reductant may be thermally decomposed.Thus, the residual reductant deposits within the SCR system 52 may besubstantially removed from the system allowing for the inlet SCR NOxamount and the outlet SCR NOx amount to be approximately the same.Mechanical purging may be from an operator or service technicianphysically removing the SCR system 52 and cleaning it (i.e.,substantially removing any particulate matter and reductant deposits).

To illustrate the functionality of the engine module 105, FIGS. 4-5 arenow referenced. FIG. 4 depicts graphs of a selective catalytic reductionsystem service diagnostic test according to an example embodiment. Aspeed versus time graph 400 and a temperature versus time graph 410 ofthe SCR system diagnostic test are shown. The graph 400 depicts theengine speed of an engine from engine speed commands provided by theengine module 105. In the example diagnostic test of FIG. 4, a warm-upprocess 402 initiates the diagnostic process. During this process, theengine module 105 maintains a relatively high engine speed (e.g., 1000RPM) for a relatively long period of time (e.g., approximately twentyminutes). As shown in graph 410, the warm-up process corresponds with anincrease in exhaust temperature (e.g., greater than 500 degreesCelsius). In other embodiments, the purging process may take a longer(e.g., a 25 minute, etc.) or a shorter (e.g., a 15 minute, etc.) periodof time to thermally purge the reductant deposits. Similarly, based onthe engine used or other application, the engine speed may be greaterthan, less than, or equal to the example depicted in FIG. 4. In anyevent, the warm-up process 402 corresponds with the substantial removalof reductant deposits in the SCR system. During this warm-up or purgingprocess 402, the dosing module 104 has suspended dosing.

At a predetermined time after the purging process, the engine module 105further increases the speed of the engine (portion 404). The excitationportion 404 of graph 400 shows how the engine module 105 affects theengine out NOx amount via an increase in engine speed. A closer lookinto the effect of engine speed on NOx emissions may be seen in FIG. 5.

FIG. 5 depicts a graph 500 of SCR inlet NOx sensor data, such as SCRinlet NOx data 112, and SCR outlet NOx sensor data, such as SCR outletNOx sensor data 114, as a function of ignition timing and engine speed.More particularly, FIG. 5 shows how the engine module 105 may affect theengine out NOx amount (and, consequently, the NOx amount measured by theSCR inlet NOx sensor 55 (curve 502) and the SCR outlet NOx sensor 57(curve 504)) by commanding at least one of an adjustment to engine speedand ignition timing. In this example, the engine out NOx excitementbegins after the purging process. In this example, the engine module 105adjusts the engine out NOx amount after approximately twelve hundredseconds. In various other embodiments, as mentioned above, the purgingprocess may be shorter or longer, such that the engine out NOxadjustment occurs at a different point in time. Thus, in the exampleshown, after a predetermined amount of time (e.g., 1240 seconds) theengine module 105 advances the ignition timing (portion 506). Followingthis first NOx excitation command, the engine module 105 increases theengine speed (portion 508). In other embodiments, the excitations of theengine out NOx amount may be induced/caused by any of the abovementioned commands provided by the engine module 105 (e.g.,advancing/retarding ignition timing, increasing/decreasing engine speed,post-combustion fuel injections, etc.). Also, the order, timing, andduration of the engine out NOx commands may change. For example, theengine speed may be increased followed by the advance of ignition timingor the ignition timing and engine speed may be increased and advancedsimultaneously. Also, the NOx excitation process may include any numberof engine out NOx excitation events (e.g., one, two, three, five, eight,etc.).

In this example, the first NOx excitation 506 is caused by an advancedignition timing command. The advanced ignition timing causes the NOxlevels in the exhaust to increase from 170 parts-per-million (ppm) toover 300 ppm, as is shown in the graph 500. In other embodiments, theexcitation may be caused by retarding the ignition timing command.Retarding the ignition timing command may cause the NOx levels in theexhaust to decrease. As shown, a second excitation 508 at approximately1300 seconds is caused by an increase engine speed command correspondingwith the excitation portion 404 (FIG. 4). The increase in engine speedcauses the NOx levels in the exhaust to increase from 170 ppm to 500ppm. In other embodiments, the excitation may be caused by a reductionin engine speed which may cause the NOx levels in the exhaust todecrease. In other embodiments, the rates at which the NOx levelsincrease (or decrease) and by how much may vary (e.g., the NOx levelsmay rise from 170 ppm to 250 ppm in 8 seconds, etc.). One purpose of theexcitation is to quantify how the sensors react to the rapidly changingNOx levels to determine if they are effective in monitoring NOx in theexhaust flow. In other words, the engine 20 is manipulated to provide aricher NOx signal which contains more useful diagnostic information.

Referring back to FIG. 2, it should be understood that other parametersmay also be controlled by the engine module 105. Generally speaking,however, the engine module 105 is structured to adjust one or moreparameters that affect a NOx amount emitted from the engine, as well aspurge any residual reductant within the SCR system 52. Accordingly,although engine speed and engine timing are described as independentevents, these events may be collectively commanded. Similarly,additional actuation commands may also be provided by the engine module105 that alter/change the NOx emission levels out of the engine and thatsubstantially purge the reductant deposits in the SCR system 52.

The SCR inlet NOx module 106 is structured to receive and store the SCRinlet NOx data 112 entering the SCR system (e.g., SCR system 52). Thus,the SCR inlet NOx module 106 may be communicably coupled to the SCRinlet NOx sensor 55. The SCR outlet NOx module 107 is structured toreceive and store the SCR outlet NOx data 114 exiting the SCR system.Thus, the SCR outlet module 107 may be communicably coupled to the SCRoutlet NOx sensor 57. The rate at which the NOx data (e.g., the SCRinlet NOx data 112, the SCR outlet NOx data 114, etc.) may be measuredand stored within each of the modules 106 and 107 may be dependent onthe sampling rate of the respective NOx sensors being used in theexhaust aftertreatment system 22. In one embodiment, the NOx data may beacquired at a rate substantially close to the maximum sampling rate ofthe sensors. In other embodiments, the NOx data may be measuredperiodically (e.g., every 5 seconds, etc.). The sampling rate may bepredefined within the controller 100 or a user may define the samplingrate via the operator I/O device 120. The NOx data acquired and storedby both modules 106 and 107 may be provided to the phase correctionmodule 108 and the system diagnostic module 109 to diagnose one or morecomponents of the exhaust aftertreatment system 22, which is describedmore fully herein.

In other embodiments, an additional controller module may be includedsuch as an AMOx outlet NOx module. The modules 106, 107, and the AMOxoutlet NOx module are structured to receive measured NOx data. The NOxdata includes at least one of a SCR inlet NOx amount, a SCR outlet NOxamount, and an AMOx outlet NOx amount. Accordingly, the NOx data may bemeasured in real time or substantially real time by NOx sensors 55, 57,and 14. The measured NOx data provides an indication of the NOx amountin the exhaust gas stream entering and leaving the SCR system 52 (insome embodiments, the AMOx 60).

The phase correction module 108 is structured to receive the SCR inletNOx data 112 and the SCR outlet NOx data 114 from modules 106 and 107.The phase correction module 108 is also structured to determine a phaseshift between the measured SCR inlet and outlet NOx data 112 and 114.The phase shift may be described as follows. The timing in which the SCRinlet and outlet NOx sensors 55 and 57 measure NOx levels is subject toa transport delay due to the exhaust flowing from the SCR inlet NOxsensor 55 to the SCR outlet NOx sensor 57. Transport delay refers to thetime or duration in which it takes an amount of the exhaust gas totravel from the SCR inlet NOx sensor 55 to the SCR outlet NOx sensor 57.For example, it may take the exhaust gas X seconds to travel through theSCR system 52. Therefore, the SCR outlet NOx data 114 (e.g., NOxamounts, etc.) measured by the outlet sensor may be shifted by X secondswhen compared to the SCR inlet NOx data 112. The transport delay mayalso be a function of the response time of the sensors used in theexhaust aftertreatment system 22. According to one embodiment, thetransport delay between the SCR inlet NOx data 112 and the SCR outletNOx data 114 may be determined by using a cross-correlation functionwhich is described more fully herein. However, in certain otherembodiments, other functions may be utilized to determine the transportdelay.

To aid explanation of transport delay, referring now to FIGS. 6-7, FIG.6 depicts a comparison of the SCR inlet and the outlet NOx data (e.g.,the SCR inlet NOx data 112 and the SCR outlet NOx data 114, etc.) withthe effects of transport delay according to one embodiment. Transportdelay may be referred to herein as phase lag or phase shift.Additionally, transport delay may be referred to in the time domain astime lag or time shift. Still referring to FIG. 6, a graph 600 shows ascatter of diagnostic data 610 around an ideal response 630. Thediagnostic data 610 refers to the SCR inlet and outlet NOx data measuredand accumulated by the modules 106 and 107. The ideal response 630 isdefined as ideal because it represents diagnostic data in which the SCRinlet NOx sensor 55 and the SCR outlet NOx sensor 57 measure identicalNOx data. For example, in an ideal test, all of the reductant depositsare purged from the SCR system 52. This causes the SCR inlet NOx to beidentical to the SCR outlet NOx. Also, in an ideal response, a phase lagbetween the sensors is not present. Accordingly, the ideal response 630corresponds with a line representing SCR NOx outlet data versus SCR NOxinlet data having a slope of one. Comparatively, the scatter of thediagnostic data 610 around the ideal response 630 is caused by the phaselag of the downstream sensor (the SCR outlet NOx sensor 57) relative tothe SCR inlet NOx sensor. Due to the diagnostic data 610 substantiallynot following the ideal response 630, the phase correction module 108determines that the inlet and outlet NOx data are out-of-phase and aphase shift is determined by the phase correction module 108.

The phase (or time) shift refers to the transport delay duration (i.e.,the duration it takes an amount of exhaust gas to travel from the SCRinlet NOx sensor to the SCR outlet NOx sensor). FIG. 7 depicts a graphof a cross-correlation function of the SCR inlet NOx data and the SCRoutlet NOx data (e.g., the SCR inlet NOx data 112 and the SCR outlet NOxdata 114, etc.) used to determine a time shift between the SCR inlet andoutlet NOx measurements according to one embodiment. More particularly,FIG. 7 shows how the phase correction module 108 may determine the phaseshift between the SCR inlet and outlet NOx measurements. The dynamics ofthe NOx sensors are substantially impacted by the transport delay. Thephase correction module 108 may utilize various numerical methods (e.g.,a cross-correlation function, etc.) or any other processes or methods todetermine the phase shift of the SCR outlet NOx data relative to the SCRinlet NOx data (e.g., diagnostic data 610) brought upon by the transportdelay. In this example, a cross-correlation function may be utilized bythe phase correction module 108 to determine the transport delay (i.e.,time lag, phase shift, etc.) between the measurements of exhaust flowcharacteristics (e.g., NOx emissions) along the exhaust aftertreatmentsystem 22. After applying a cross-correlation function between the twosignals, the phase correction module 108 may determine a maximum of thecross-correlation function. The maximum indicates the point in timewhere the signals (the SCR inlet NOx measurement signal and the SCRoutlet NOx measurement signal) are best aligned. In this example, agraph 700 shows a cross-correlation analysis between the SCR inlet NOxdata and the SCR outlet NOx data presented in FIG. 6. By implementing across-correlation function, the transport delay between the two sets ofdata may be determined from the cross-correlation maximum 703. Lookingat an enlarged view 702 of the cross-correlation maximum 703, a timeshift 704 may be quantified by determining the horizontal shift of thecross-correlation maximum 703 from a vertical axis 701. The time shift704 represents the transport delay between the measurements provided bythe SCR inlet and outlet NOx sensors. In the example, the phase shift704 between the SCR inlet and outlet NOx data is approximately 1.6seconds. In other embodiments, the time lag between the two sensors maybe shorter or longer depending on the relative response time of thesensors and the dimensions of the SCR system 52 (i.e., the distancebetween the SCR inlet and outlet NOx sensors 55 and 57).

Based on the determined time shift, the phase correction module 108 isstructured to apply the time or phase shift to the SCR outlet NOx data114. In one embodiment, the application of the phase shift by the phasecorrection module 108 is performed by shifting the SCR outlet NOx data114 by the determined phase shift. In this example, with the determinedphase shift from FIG. 7 of 1.6 seconds, the diagnostic data 610(specifically, the SCR outlet NOx data) may be shifted by that amount.Therefore, the data accumulated prior to 1.6 seconds by the SCR outletNOx sensor 57 may be removed and the remaining data may be shiftedaccordingly (e.g., the data point previously at 1.6 seconds may now bethe data point at zero seconds, etc.). Also, an equivalent number ofdata points may be removed from the last measurements made by the SCRinlet NOx sensor 55. This phase shift correction allows for the gascomposition at each time interval to be substantially equivalent forboth the inlet and outlet NOx sensors. This results in the transportdelay between the inlet and outlet NOx sensors being substantiallyminimized, causing the transport delay to have minimal effect on the NOxsensor diagnostic test of the present disclosure.

To summarize, as the diagnostic test on the SCR inlet and outlet NOxsensors 55 and 57 is performed, the sensors may be measuring datasimultaneously. However, the data being measured by each sensor may beof differing gas compositions due to the transport delay. For example,at time X, the SCR inlet sensor 55 may measure a certain amount of NOxin the exhaust gas. The amount or sample of exhaust gas at the inlet maybe different from the amount or sample of exhaust measured by the SCRoutlet sensor 57 at time X due to the transport delay. Therefore, theSCR outlet NOx data 114 measured by the outlet sensor may be correctedby the determined time shift (from the transport delay effects) so thatthe data at time X corresponds to the substantially same gas compositionor sample at both sensors, which may allow for a substantially improveddiagnostic analysis.

After application of the determined phase shift by the phase correctionmodule 108 on the SCR outlet NOx data 114, the system diagnostic module109 is structured to determine a diagnostic feature based on the SCRinlet NOx data 112 and the phase shifted SCR outlet NOx data 114. Thesystem diagnostic module 109 is structured to determine a state of theSCR inlet and outlet NOx sensors based on the diagnostic feature,wherein the state includes at least one of both of the SCR inlet andoutlet NOx sensors are operational and at least one of the SCR inlet andoutlet NOx sensors are faulty. This determination, detailed descriptionsof faulty states, and other features are explained more fully herein.

The diagnostic feature may include at least one of a first diagnosticfeature and a second diagnostic feature. The first diagnostic featuremay include a gain diagnostic feature. The second diagnostic feature mayinclude a correlation coefficient diagnostic feature. The gaindiagnostic feature refers to how close the inlet and outlet NOx sensormeasurements are to one another. In one embodiment, the gain diagnosticfeature may be determined by plotting the phase shifted SCR outlet NOxdata 114 versus SCR inlet NOx data 112 and performing a least-squareslinear regression of the plotted data while setting the y-intercept tozero. The slope of the resulting line represents the gain diagnosticfeature. If the SCR inlet and outlet NOx data 112,114 are identical(i.e., an ideal case) or substantially identical, the gain (or slope) isone or may approach one. However, if the SCR outlet NOx data 114 are afactor of X (e.g., 3) less than the SCR inlet NOx data 112, the gain ofthe line is 1/X (e.g., ⅓). In other embodiments, the gain diagnosticfeature may be determined using any other statistical methods which maydetermine the slope of data (e.g., inlet and phase shifted outlet NOxdata).

The correlation coefficient diagnostic feature refers to the degree towhich a linear relationship exists between the measured SCR inlet NOxdata 112 and the phase shifted SCR outlet NOx data 114. For example, asubstantially linear relationship may result in a correlationcoefficient of 0.99 or higher. According to one embodiment, thecorrelation coefficient diagnostic feature may be determined as follows:

$\begin{matrix}{r = \frac{{n{\sum{xy}}} - {\left( {\sum x} \right)\left( {\sum y} \right)}}{\sqrt{{n\left( {\sum x^{2}} \right)} - \left( {\sum x} \right)^{2}}\sqrt{{n\left( {\sum y^{2}} \right)} - \left( {\sum y} \right)^{2}}}} & \lbrack 2\rbrack\end{matrix}$

where r is the correlation coefficient diagnostic feature, x is the SCRinlet NOx data 112 measured by the SCR inlet NOx sensor 55, y is the SCRoutlet NOx data 114 measured by the SCR outlet NOx sensor 57, and n isthe number of data pairs measured by the inlet and outlet NOx sensors. Apositive correlation infers that the change in one variable may predicta change in the same direction in the second variable. For example, asengine out NOx amount increases from an increase in engine speed or anadvance in ignition timing, both the inlet and outlet NOx sensors mayalso measure a relative increase. A negative correlation infers that achange in one variable means a change in the second variable in theother direction. A correlation coefficient of zero indicates that thereis no discernable relationship between the SCR inlet and phase shiftedoutlet NOx data 112,114. For example, as engine out NOx amountsfluctuate, one sensor may measure the relative changes while the othersensor measures constant NOx levels (e.g., a stuck in-range error). Dueto the faulty sensor, a substantially non-linear relationship betweenthe inlet and outlet NOx measurements may be present, causing thecorrelation coefficient between the two data sets to be substantiallyzero or less than zero (i.e., negative).

To illustrate how the system diagnostic module 109 may determine thegain and correlation coefficient diagnostic features, FIG. 8 is nowreferenced. FIG. 8 depicts SCR inlet versus outlet NOx data (e.g., theSCR inlet NOx data 112 and the SCR outlet NOx data 114, etc.) with anapplied phase shift correction according to one embodiment. As shown,the diagnostic data 810 (i.e., phase shift corrected diagnostic data610) is relatively more linear than the diagnostic data 610, which isdue to the implementation of the phase shift. As mentioned above, fromthe system diagnostic module 109 applying a least-squares linearregression with a y-intercept of zero and equation [2], the gain andcorrelation coefficient may be determined. From performing theregression, a least-squares linear regression line 820 is fit to thediagnostic data 810. In turn, in this example, the gain and correlationcoefficient are determined by the system diagnostic module 109 to be0.94 and 0.99. Therefore, as described more fully herein, the systemdiagnostic module 109 determines a state of the SCR inlet and outlet NOxsensor based on the diagnostic features. In this example, the module 109determines the sensors to be functioning properly (i.e., operational)and are likely not the cause of a potential low observed efficiency ofthe SCR catalyst 50.

As mentioned above, based on at least one of the first and seconddiagnostic feature determined by the system diagnostic module 109, thesystem diagnostic module 109 is structured to determine the state of thesensors: operational, inconclusive results, or faulty. An operationalstate corresponds with the NOx sensors functioning properly. Accordingto one embodiment, the system diagnostic module 109 is structured todetermine that the SCR inlet and outlet NOx sensors are operationalbased on the correlation coefficient diagnostic feature being greaterthan or equal to an operational correlation coefficient diagnosticfeature threshold and the gain diagnostic feature being within a set ofoperational gain diagnostic feature parameters. In one embodiment, thisdetermination corresponds with the gain being greater than or equal to0.90 but less than or equal to 1.10 (i.e., the set of operational gaindiagnostic feature parameters) and the correlation coefficient beinggreater than or equal to 0.98 (i.e., the operational correlationcoefficient diagnostic feature threshold). Therefore, in a scenario withproperly functioning SCR NOx sensors, there may be a highly linearrelationship between the two data sets and a substantially idealresponse (i.e., both sensors reading substantially equal values) asshown in FIG. 8.

The system diagnostic module 109 may also determine that the results areinconclusive. Inconclusive results may correspond with reductantdeposits being detected. When reductant deposits are detected, the gaindiagnostic feature indicates that a substantially non-ideal relationship(i.e., slope) exists between the SCR inlet and the phase shifted SCRoutlet NOx data 112,114 with a non-linear relationship also existingbased on the determined correlation coefficient diagnostic feature.According to one embodiment, the diagnostic module 109 determines thatthe results are inconclusive based on the correlation coefficientdiagnostic feature being within a set of inconclusive correlationcoefficient diagnostic feature parameters and the gain diagnosticfeature being less than an inconclusive gain diagnostic featureparameter. In one embodiment, this situation corresponds with the gaindiagnostic feature being less than 0.90 (i.e., the inconclusive gaindiagnostic feature parameter) and the correlation coefficient being lessthan 0.98 but greater than zero (i.e., the set of inconclusivecorrelation coefficient diagnostic feature parameters). According toother embodiments, the gain and correlation diagnostic feature valuesthat indicate an inconclusive state may differ from that mentionedabove. For example, the gain may be substantially lower than one due tothe presence of reductant in the SCR catalyst 50 reacting with the NOxin the exhaust gas, reducing the NOx to less harmful emissions. Thisreduction may cause the inlet NOx amount to be substantially more thanthe outlet NOx amount, which may cause the gain diagnostic feature to besubstantially less than one. Also, the relatively poor correlationcoefficient may be caused by the reductant deposits being present andcontinually being purged (i.e., thermally decomposed) throughout the NOxexcitation process (see, e.g., FIG. 12). Thus, the SCR outlet NOx sensor57 may continually measure the amount of NOx throughout the diagnosticprocess in a non-linear fashion (e.g., exponentially, etc.), resultingin a non-linear relationship between the SCR inlet and the outlet NOxdata 112,114.

To demonstrate the non-linearity between inlet and outlet NOxmeasurements when reductant deposits are present, FIG. 12 is nowreferenced. FIG. 12 depicts a graph 1200 of changing NOx conversionbetween inlet NOx sensor data and outlet NOx sensor data (e.g., the SCRinlet NOx data 112 and the SCR outlet NOx data 114, etc.) according toone embodiment. An outlet NOx sensor data curve 1204 continuallyapproaches an inlet NOx sensor data curve 1202 as time progresses duringthe diagnostic test. For example, at time 1000 seconds, the differencein magnitude of the curves 1202 and 1204 is approximately 150 ppm. Whileat 1900 seconds, the difference between the curves 1202 and 1204 isdecreased substantially to less than 50 ppm. As mentioned above, whenthe SCR outlet NOx sensor measures NOx data in a non-linear fashion(e.g., due to reductant deposits), as in FIG. 12, a non-linearrelationship between the inlet and outlet NOx data may result.Therefore, conclusive results on the functionality of the inlet andoutlet NOx sensors may be unable to be determined and additional purgingof the deposits may need to be done.

To further illustrate the inconclusive results state, FIG. 11 is nowreferenced. FIG. 11 depicts a graph of outlet NOx sensor data versusinlet NOx sensor data (e.g., the SCR inlet NOx data 112 and the SCRoutlet NOx data 114, etc.) with reductant deposits present in theaftertreatment system between the NOx inlet and NOx outlet according toone embodiment. A graph 1100 includes the ideal response 630, diagnosticdata 1110, and a least-squares linear regression line 1120. Fitting theleast-squares linear regression line 1120 to the diagnostic data 1110and applying equation [2] results in a gain of 0.42 and a correlationcoefficient of 0.95. As a result, the system diagnostic module 109determines the results to be inconclusive. According to one embodiment,system diagnostic module 109 provides a command to rerun the diagnosticprocedure. If reductant is present in the SCR system, the SCR inlet andoutlet NOx sensors 55 and 57 may not measure the same exhaustcomposition, resulting in data which is not approximately the same. Theunsuccessful purging of the reductant deposits within the SCR system maylead to inconclusive results for the NOx sensor diagnostic test.Therefore, the remaining reductant may need to be purged, NOx dataacquired again, a phase shift determined, and diagnostic featuresdetermined once again.

Referring back to FIG. 2, the system diagnostic module 109 may furtherdetermine that a faulty state exists with at least one of the SCR inletand outlet NOx sensor. A faulty state may indicate that at least one ofthe SCR inlet and outlet NOx sensors 55 and 57 are operating incorrectly(e.g., detecting wrong amounts of NOx, be miscalibrated causing wrongamounts of NOx to be detected, etc.). This state may correspond withgain and correlation values outside of both the inconclusive ranges andthe operational ranges. In one example, the system diagnostic module 109is structured to determine that at least one of the SCR inlet NOx sensorand the SCR outlet NOx sensor are in a faulty state based on thecorrelation coefficient diagnostic feature being less than or equal to acorrelation coefficient diagnostic feature threshold. According to oneembodiment, the correlation coefficient diagnostic feature thresholdzero. According to other embodiments, the correlation coefficientdiagnostic feature threshold may be another value. The selection of thisvalue may be configurable by the I/O device 120 and vary fromapplication-to-application.

According to one embodiment, the faulty state may include, but is notlimited to, three failure modes: an out-of-range error (high or low), anin-range error (high or low), and a stuck in-range error. According toone embodiment, the system diagnostic module 109 is structured todetermine that at least one of the SCR inlet and outlet NOx sensors isfaulty based on the correlation coefficient diagnostic feature beinggreater than or equal to an out-of-range correlation coefficientdiagnostic feature threshold and the gain diagnostic feature being atleast one of greater than or equal to a high out-of-range gaindiagnostic feature parameter and within a set of low out-of-range gaindiagnostic feature parameters. In one embodiment, the out-of-range errorcorresponds with the gain being at least one of greater than or equal to3.0 (i.e., the high out-of-range gain diagnostic feature parameter) andless than or equal to 0.33 but greater than zero (i.e., the set of lowout-of-range gain diagnostic feature parameters) and the correlationcoefficient being greater than or equal to 0.98 (i.e., the out-of-rangecorrelation coefficient diagnostic feature threshold).

According to one embodiment, the system diagnostic module 109 isstructured to determine that at least one of the SCR inlet and outletNOx sensors is faulty based on the correlation coefficient diagnosticfeature being greater than or equal to an in-range correlationcoefficient diagnostic feature threshold and the gain diagnostic featurebeing within at least one of a set of high in-range gain diagnosticfeature parameters and a set of low in-range gain diagnostic featureparameters. In one embodiment, the in-range error corresponds with thegain being at least one of between 1.10 and 3 (i.e., the set of highin-range gain diagnostic feature parameters) and between 0.33 and 0.90(i.e., the set of low in-range gain diagnostic feature parameters) andthe correlation coefficient being greater than or equal to 0.98 (i.e.,the in-range correlation coefficient diagnostic feature threshold). If ahigh in-range or high out-of-range error exists, at least one of the SCRoutlet NOx sensor 57 and the SCR inlet NOx sensor 55 may be faulty. TheSCR outlet NOx sensor 57 may be measuring high and the SCR inlet NOxsensor 55 may be measuring low amounts of NOx. If a low in-range or lowout-of-range error exists, at least one of the SCR outlet NOx sensor 57and the SCR inlet NOx sensor 55 may be faulty. The SCR outlet NOx sensor57 may be measuring low and the SCR inlet NOx sensor 55 may be measuringhigh amounts of NOx. For example, as the NOx levels are excited, onesensor may be functioning properly and measuring the correct amounts ofNOx in the exhaust. While the second sensor may have a calibration erroror defect which causes it to measure NOx levels substantially higher orlower than the true amount.

According to one embodiment, the system diagnostic module 109 isstructured to determine that at least one of the SCR inlet and outletNOx sensors is faulty based on the correlation coefficient diagnosticfeature being less than or equal to a stuck in-range correlationcoefficient diagnostic feature threshold. In one embodiment, the stuckin-range failure mode corresponds with the correlation coefficient beingless than zero or substantially zero (i.e., the stuck in-rangecorrelation coefficient diagnostic feature threshold). For this failuremode, as the NOx levels are excited, one sensor may be functioningproperly and measuring substantially correct amounts of NOx in theexhaust gas while the second sensor may have some sort of defect whichcauses it to measure NOx levels in the same range regardless of theexcited levels of NOx in the exhaust as commanded by the engine module105. For example, if the NOx amount is fluctuating between zero ppm and2500 ppm, a sensor with a stuck in-range error may continually measuredata in a range between 1200 and 1300 ppm. Therefore, a positive linearrelationship may not exist between the inlet and outlet data causing thecorrelation coefficient diagnostic feature to be substantially zero orless than zero.

To further demonstrate the failure modes, FIGS. 9-10 are now referenced.FIG. 10 depicts a graph of outlet NOx sensor data versus inlet NOxsensor data (e.g., the SCR inlet NOx data 112 and the SCR outlet NOxdata 114, etc.) for a failed NOx outlet sensor according to oneembodiment. In this example, a graph 1000 includes the ideal response630, diagnostic data 1010, and a least-squares linear regression line1020. Fitting the least-squares linear regression line 1020 and applyingequation [2] to the diagnostic data 1010 results in a gain of 0.48 and acorrelation coefficient of 0.99. Therefore, based on the above definedfailure modes, this failure is a low in-range error. The low in-rangeerror may mean that the failure is in the SCR outlet NOx sensor 57, suchthat the outlet sensor is reading a lower than actual NOx amount (e.g.,half). In other embodiments, the low in-range error may indicate failurefor a SCR inlet NOx sensor 55, such that the inlet sensor is reading ahigher than actual NOx amount (e.g., double). Therefore, since a failureof either the inlet or outlet NOx sensor may cause a fault code, it maynot be possible to know which sensor is faulty and both sensors may needto be changed. In other embodiments, the gain and correlationcoefficient may vary for this type of failure mode as long as eachremains within the limits defined above.

Referring now to FIG. 9, a series of graphs depicting various failuremodes for NOx inlet and outlet sensors are shown. A graph 900 shows aNOx data versus time relationship for a stuck in-range sensor failure. Areference signal 902 may be applied to a sensor with a stuck in-rangeerror and a result like that of a sensor reading 904 may result. Asshown, as the reference signal 902 fluctuates, the sensor reading 904remains relatively constant. For example, during the excitation of theNOx levels via at least one of ignition timing and engine speed, one ofthe SCR NOx sensors may have a stuck in-range failure. Therefore, onesensor may read the correct NOx levels and the other may lack anyresponse to the excitations and stay relatively constant. This type ofresponse lacks any sort of correlation between the inlet and outlet dataand may flag a fault code.

A graph 910 shows a NOx data versus time relationship for a low in-rangesensor failure. The reference signal 902 may be applied to a sensor witha low in-range error and a result like that of a sensor reading 914 mayresult. As shown, as the reference signal 902 fluctuates, the sensorreading 914 fluctuates in the same manner, however at an amount half ofthe reference signal. A graph 920 shows substantially the same responseas the graph 910 except it is a representation of a low out-of-rangesensor failure. A sensor reading 924 fluctuates in the same manner asthe sensor reading 914, however at an amount one-fourth of the referencesignal. In either case, one of the sensors may be miscalibrated orfaulty and the failed sensor may measure the changes in NOx levels, justat an incorrect proportion of the true amount.

Referring back to FIG. 2, based on the state determined by the systemdiagnostic module 109, the notification module 110 is structured toprovide one or more notifications (e.g., fault codes). The notificationsmay correspond with a fault code, a notification (e.g., on the operatorI/O device 120), and the like. The notification indicates the state ofthe SCR inlet and outlet NOx sensors 55 and 57. In the case of anoperational state, the notification module 110 may supply a notificationto the via the operator I/O device 120 to run diagnostic tests on othercomponents of the exhaust aftertreatment system 22 that may cause a lowSCR efficiency (e.g., the DEF dosing system, the DOC/DPF unit, and theSCR/AMOx catalyst unit) to determine the actual cause of the low SCRefficacy. Following an inconclusive results type of detection, thenotification module 110 may notify the service technician to re-run thediagnostic testing due to reductant deposit detection. With any of thefailure modes, the notification module 110 may supply a notification tothe operator to replace the SCR NOx sensors due to faulty performance.

Referring now to FIG. 3, a method 300 of performing NOx sensorrationality diagnostics for an exhaust aftertreatment system accordingto an example embodiment. In one example embodiment, method 300 may beimplemented with the controller 100 of FIG. 1. Accordingly, method 300may be described in regard to FIGS. 1-2.

At process 301, the controller 100 provides a dosing command to suspendreductant dosing in the exhaust aftertreatment system 22. According toone embodiment, in order to perform a NOx sensor rationality diagnosticacross the SCR system, the reductant needs to be suspended so that theinlet and outlet NOx levels are substantially equivalent during the timeof the diagnostic testing. For example, if the reductant dosing is notsuspended, the ammonia in the reductant may react with NOx in thepresence of the SCR catalyst 50 and reduce the NOx to less harmfulemissions, such as N₂ and H₂O. In this case, it may not be possible todeduce a credible state of the SCR inlet and outlet NOx sensors 55 and57 since they may be measuring different exhaust compositions. Measuringdifferent exhaust compositions declines the ability to perform arational diagnostic test of the inlet and outlet NOx sensors.

At process 302, the controller 100 provides a command to purge thereductant deposits within the SCR system. The purging of the reductantdeposits may be done either mechanically or by decomposing the reductantdeposits via an increase in temperature (i.e., thermally). Mechanicalpurging may include a technician physically removing all orsubstantially all the reductant deposits in the SCR system. Thermalpurging may include providing one or more commands to the engine systemto increase the exhaust gas temperatures. This causes the exhaust gastemperatures to be relatively warmer while flowing through the SCRsystem. In turn, the relatively warmer exhaust gas temperatures may burnoff or purge the reductant deposits in the SCR system. The commands mayinclude, but are not limited to, increasing engine speed, advancingignition timing, a post-combustion fuel injection, and any other commandthat increases the exhaust gas temperature.

At process 303, the controller 100 provides a command to adjust anengine out NOx amount. By affecting the engine out NOx amount, theamount of NOx measured by the NOx sensors may also change. According toone embodiment, the command may include, but is not limited to, anadjustment to ignition timing, an adjustment to engine speed, and anyother command that affects or adjusts an engine out NOx amount. Asmentioned above, the ignition timing may be at least one of advanced andretarded and the engine speed may be at least one of increased anddecreased. Any of these changes may cause an adjustment to the NOxlevels in the exhaust flow. For example, increases in NOx levels may becaused by at least one of advancing ignition timing and increasingengine speed. While decreases in NOx levels may be caused by at leastone of retarding ignition timing and reducing engine speed. Theexcitation of NOx levels may only last seconds (e.g., 30 to 60 seconds)in some embodiments, while in other embodiments it may last minutes(e.g., 1 to 5 minutes or longer). During the excitation process, the SCRinlet and outlet NOx sensors 55 and 57 may measure the changes in theNOx levels.

At process 304, the controller 100 interprets the measured SCR inlet andoutlet NOx data (e.g., the SCR inlet NOx data 112 and the SCR outlet NOxdata 114, etc.) from the SCR inlet and outlet NOx sensors. This data maybe stored in the SCR inlet and outlet NOx modules 106 and 107 to beutilized by the phase correction module 108. At process 305, thecontroller 100 determines a phase shift between the inlet and outletmeasured NOx data. The phase shift represents a duration for an amountof exhaust gas to travel from the SCR inlet NOx sensor to the SCR outletNOx sensor. For example, as the NOx levels are excited, the inlet andoutlet SCR NOx sensors may record data out-of-phase due to the transportdelay of the exhaust traveling from the inlet to the outlet of the SCRsystem. To account for this phase shift (i.e., time shift), astatistical function (e.g., cross-correlation function, cross-covariancefunction, etc.) may be applied to determine the phase shift. Thedetermined phase shift is applied to the SCR outlet NOx data at process306.

At process 307, the controller 100 determines a diagnostic feature basedon the SCR inlet NOx data and phase shifted SCR outlet NOx data. Thediagnostic feature provides an indication of a state regarding the SCRinlet and outlet NOx sensors 55 and 57. As mentioned above, the state ofthe SCR inlet and outlet NOx sensors may include operational,inconclusive results, or faulty. As also mentioned above, the diagnosticfeature may include at least one of a gain diagnostic feature and acorrelation coefficient diagnostic feature. Example processdeterminations regarding the state of at least one of the SCR inlet andoutlet NOx sensors are shown in processes 308 and 310-313.

At process 308, the controller 100 determines reductant deposits arepresent in the SCR system 52 based on the gain diagnostic feature beingless than the inconclusive gain diagnostic feature parameter (e.g.,0.90) and the correlation coefficient being within the set ofinconclusive correlation coefficient diagnostic feature parameters(e.g., 0 to 0.98). If this state is detected, a notification (process309) may appear in front of the operator or service technician via theoperator I/O device 120. This particular notification instructs thetechnician to re-run the diagnostic test (processes 301-307) due toreductant deposit detection.

Processes 310-313 determine the state of the SCR NOx sensors (e.g.,faulty such as having an out-of-range error (high or low), an in-rangeerror (high or low), and a stuck in-range error, or operational) basedon the above defined gain and correlation coefficient for the failuremodes and operational state. For processes 310-312, each processdetermines that at least one of the SCR inlet NOx sensor and the SCRoutlet NOx sensor are faulty. At process 310, the controller 100determines a SCR NOx sensor in-range error exists based on thecorrelation coefficient being greater than or equal to an in-rangecorrelation coefficient diagnostic feature threshold (e.g., 0.98) andthe gain diagnostic feature being within the set of in-range gaindiagnostic feature parameters (e.g., 0.33 to 0.90 or 1.10 to 3.0). Atprocess 311, the controller 100 determines a SCR NOx sensor out-of-rangeerror exists based on the correlation coefficient being greater than orequal to the out-of-range correlation coefficient diagnostic featurethreshold (e.g., 0.98) and the gain being either greater than or equalto the high out-of-range gain diagnostic feature parameter (e.g., 3.00)or within the set of low out-of-range gain diagnostic feature parameters(e.g., 0 to 0.33). At process 312, the controller 100 determines a SCRNOx sensor stuck in-range error exists based on the determinedcorrelation diagnostic feature being less than or equal to the stuckin-range correlation coefficient diagnostic feature threshold (e.g.,zero). Therefore, for processes 310-312, the controller 100 may supply anotification to a technician via the operator I/O device 120 to replacethe SCR inlet and outlet NOx sensors 55 and 57 (process 314). However,for process 313, the controller 100 determines the SCR inlet and outletNOx sensors are operational based on the correlation coefficientdiagnostic feature being greater than or equal to the operationalcorrelation coefficient diagnostic feature threshold (e.g., 0.98) andthe gain diagnostic feature being within the set of operational gaindiagnostic feature parameters (e.g., 0.90 to 1.10). Therefore, thecontroller 100 may supply a notification to the user via the operatorI/O device 120 to run various diagnostic tests on other components ofthe exhaust aftertreatment system 22 (process 314), as mentioned above.

An example implementation of the method 300 is as follows. In thisexample, the aftertreatment system is embodied in a vehicle and a lowSCR efficiency has been received by the operator of the vehicle. Toclear the fault code, the operator of the vehicle brings the vehicle toa service test center. A technician, via the controller, begins to purgethe reductant deposits in the SCR system (processes 301-302). Thecontroller then adjusts the engine out NOx amount while the SCR inletand outlet sensors are measuring the NOx amounts flowing through the SCRsystem (processes 303-304). After a predetermined amount of time, thecontroller beings the next part of the diagnostic procedure. Here, thecontroller uses the measured SCR inlet and outlet NOx data (e.g., theSCR inlet NOx data 112 and the SCR outlet NOx data 114, etc.) todetermine a phase shift for the SCR outlet NOx data (process 305) andapplies the determined phase shift to the SCR outlet NOx data (process306). In this example, the controller plots the SCR inlet NOx dataversus the phase shifted SCR outlet NOx data. Using this plot, thecontroller, determines one or more diagnostic features regarding a stateof the SCR inlet and outlet NOx sensors (process 307). For example, thecontroller may determine that SCR inlet and outlet NOx sensors areoperational based on the correlation coefficient diagnostic featurebeing greater than or equal to the operational correlation coefficientdiagnostic feature threshold (e.g., 0.98) and the gain diagnosticfeature being within the set of operational gain diagnostic featureparameters (e.g., 0.90 to 1.10). In which case, the technician mayeliminate the NOx sensors from the troubleshooting process and move ontoa next component to troubleshoot. In another example, the controller maydetermine that at least one of the SCR inlet and outlet NOx sensors arefaulty (e.g., an in-range failure mode as described above). Thecontroller provides a notification to the technician (e.g., process309). The technician may examine both sensors (e.g., their connections)and possibly replace one of the sensors. The technician may re-run thediagnostic. If the same or another failure mode regarding the SCR NOxsensors is determined by the controller, the technician may replace theother SCR NOx sensor. At this point, the technician may re-run thediagnostic to determine if the failure code is cleared. If not, thetechnician may troubleshoot other components of the aftertreatmentsystem and/or determine that the new replaced NOx sensors have a defect.

In any event, method 300 provides an intrusive diagnostic method thatenables a technician to isolate low SCR efficiency failure codes to theSCR inlet and outlet NOx sensors. In some instances, this isolation maysend the user time and money by foregoing the need to performtime-consuming and costly diagnostic procedures.

The schematic flow chart diagrams and method schematic diagramsdescribed above are generally set forth as logical flow chart diagrams.As such, the depicted order and labeled steps are indicative ofrepresentative embodiments. Other steps, orderings and methods may beconceived that are equivalent in function, logic, or effect to one ormore steps, or portions thereof, of the methods illustrated in theschematic diagrams.

Additionally, the format and symbols employed are provided to explainthe logical steps of the schematic diagrams and are understood not tolimit the scope of the methods illustrated by the diagrams. Althoughvarious arrow types and line types may be employed in the schematicdiagrams, they are understood not to limit the scope of thecorresponding methods. Indeed, some arrows or other connectors may beused to indicate only the logical flow of a method. For instance, anarrow may indicate a waiting or monitoring period of unspecifiedduration between enumerated steps of a depicted method. Additionally,the order in which a particular method occurs may or may not strictlyadhere to the order of the corresponding steps shown. It will also benoted that each block of the block diagrams and/or flowchart diagrams,and combinations of blocks in the block diagrams and/or flowchartdiagrams, can be implemented by special purpose hardware-based systemsthat perform the specified functions or acts, or combinations of specialpurpose hardware and program code.

Many of the functional units described in this specification have beenlabeled as modules, in order to more particularly emphasize theirimplementation independence. For example, a module may be implemented asa hardware circuit comprising custom VLSI circuits or gate arrays,off-the-shelf semiconductors such as logic chips, transistors, or otherdiscrete components. A module may also be implemented in programmablehardware devices such as field programmable gate arrays, programmablearray logic, programmable logic devices or the like.

Modules may also be implemented in machine-readable medium for executionby various types of processors. An identified module of executable codemay, for instance, comprise one or more physical or logical blocks ofcomputer instructions, which may, for instance, be organized as anobject, procedure, or function. Nevertheless, the executables of anidentified module need not be physically located together, but maycomprise disparate instructions stored in different locations which,when joined logically together, comprise the module and achieve thestated purpose for the module.

Indeed, a module of computer readable program code may be a singleinstruction, or many instructions, and may even be distributed overseveral different code segments, among different programs, and acrossseveral memory devices. Similarly, operational data may be identifiedand illustrated herein within modules, and may be embodied in anysuitable form and organized within any suitable type of data structure.The operational data may be collected as a single data set, or may bedistributed over different locations including over different storagedevices, and may exist, at least partially, merely as electronic signalson a system or network. Where a module or portions of a module areimplemented in machine-readable medium (or computer-readable medium),the computer readable program code may be stored and/or propagated on inone or more computer readable medium(s).

The computer readable medium may be a tangible computer readable storagemedium storing the computer readable program code. The computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, holographic,micromechanical, or semiconductor system, apparatus, or device, or anysuitable combination of the foregoing.

More specific examples of the computer readable medium may include butare not limited to a portable computer diskette, a hard disk, a randomaccess memory (RAM), a read-only memory (ROM), an erasable programmableread-only memory (EPROM or Flash memory), a portable compact discread-only memory (CD-ROM), a digital versatile disc (DVD), an opticalstorage device, a magnetic storage device, a holographic storage medium,a micromechanical storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, and/or storecomputer readable program code for use by and/or in connection with aninstruction execution system, apparatus, or device.

The computer readable medium may also be a computer readable signalmedium. A computer readable signal medium may include a propagated datasignal with computer readable program code embodied therein, forexample, in baseband or as part of a carrier wave. Such a propagatedsignal may take any of a variety of forms, including, but not limitedto, electrical, electro-magnetic, magnetic, optical, or any suitablecombination thereof. A computer readable signal medium may be anycomputer readable medium that is not a computer readable storage mediumand that can communicate, propagate, or transport computer readableprogram code for use by or in connection with an instruction executionsystem, apparatus, or device. Computer readable program code embodied ona computer readable signal medium may be transmitted using anyappropriate medium, including but not limited to wireless, wireline,optical fiber cable, Radio Frequency (RF), or the like, or any suitablecombination of the foregoing.

In one embodiment, the computer readable medium may comprise acombination of one or more computer readable storage mediums and one ormore computer readable signal mediums. For example, computer readableprogram code may be both propagated as an electro-magnetic signalthrough a fiber optic cable for execution by a processor and stored onRAM storage device for execution by the processor.

Computer readable program code for carrying out operations for aspectsof the present invention may be written in any combination of one ormore programming languages, including an object oriented programminglanguage such as Java, Smalltalk, C++ or the like and conventionalprocedural programming languages, such as the “C” programming languageor similar programming languages. The computer readable program code mayexecute entirely on the user's computer, partly on the user's computer,as a stand-alone computer-readable package, partly on the user'scomputer and partly on a remote computer or entirely on the remotecomputer or server. In the latter scenario, the remote computer may beconnected to the user's computer through any type of network, includinga local area network (LAN) or a wide area network (WAN), or theconnection may be made to an external computer (for example, through theInternet using an Internet Service Provider).

The program code may also be stored in a computer readable medium thatcan direct a computer, other programmable data processing apparatus, orother devices to function in a particular manner, such that theinstructions stored in the computer readable medium produce an articleof manufacture including instructions which implement the function/actspecified in the schematic flowchart diagrams and/or schematic blockdiagrams block or blocks.

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the present invention. Thus,appearances of the phrases “in one embodiment,” “in an embodiment,” andsimilar language throughout this specification may, but do notnecessarily, all refer to the same embodiment.

Accordingly, the present disclosure may be embodied in other specificforms without departing from its spirit or essential characteristics.The described embodiments are to be considered in all respects only asillustrative and not restrictive. The scope of the disclosure is,therefore, indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

What is claimed is:
 1. An apparatus, comprising: a dosing modulestructured to suspend dosing in an exhaust aftertreatment system; anengine module structured to provide a command to an engine to affect anengine out nitrogen oxide (NOx) amount; a selective catalytic reduction(SCR) inlet NOx module structured to interpret measured SCR inlet NOxdata from a SCR inlet NOx sensor; a SCR outlet NOx module structured tointerpret measured SCR outlet NOx data from a SCR outlet NOx sensor; aphase correction module structured to determine a phase shift betweenthe measured SCR inlet NOx data and the measured SCR outlet NOx data andapply the phase shift to the measured SCR outlet NOx amount data; and asystem diagnostic module structured to determine a diagnostic featurebased on the SCR inlet NOx data and the phase shifted SCR outlet NOxdata, wherein the system diagnostic module is structured to determine astate of the SCR inlet and outlet NOx sensors based on the diagnosticfeature, the state including at least one an operational state and atleast one of the SCR inlet and outlet NOx sensors are faulty.
 2. Theapparatus of claim 1, wherein the diagnostic feature includes a firstdiagnostic feature and a second diagnostic feature; wherein the firstdiagnostic feature is a gain diagnostic feature, the gain diagnosticfeature representing a slope of a best fit line for the phase shiftedSCR outlet NOx data and the SCR inlet NOx data; and wherein seconddiagnostic feature is a correlation coefficient diagnostic feature thatprovides an indication of a linear relationship for the SCR inlet NOxdata and the phase shifted SCR outlet NOx data.
 3. The apparatus ofclaim 2, wherein the system diagnostic module is structured to determinethat at least one of the SCR inlet NOx sensor and the SCR outlet NOxsensor are in a faulty state based on the correlation coefficientdiagnostic feature being less than or equal to a stuck in-rangecorrelation coefficient diagnostic feature threshold.
 4. The apparatusof claim 3, wherein the correlation coefficient diagnostic threshold iszero.
 5. The apparatus of claim 2, wherein the system diagnostic moduleis structured to determine that a faulty state exists with at least oneof the SCR inlet and outlet NOx sensors based on the gain diagnosticfeature being within a set of high in-range gain diagnostic featureparameters and the correlation diagnostic feature being greater than orequal to an in-range correlation coefficient diagnostic featurethreshold.
 6. The apparatus of claim 2, wherein the system diagnosticmodule is structured to determine that a faulty state exists with atleast one of the SCR inlet and outlet NOx sensors based on the gaindiagnostic feature being at least one of greater than or equal to a highout-of-range gain diagnostic feature parameter and within a set of lowout-of-range gain diagnostic feature parameters and the correlationdiagnostic feature being greater than or equal to an out-of-rangecorrelation coefficient diagnostic feature threshold.
 7. The apparatusof claim 2, wherein the system diagnostic module is structured todetermine that a faulty state exists with at least one of the SCR inletand outlet NOx sensors based on the gain diagnostic feature fallingwithin a set of low in-range gain diagnostic feature parameters and thecorrelation diagnostic feature being greater than or equal to anin-range correlation coefficient diagnostic feature threshold.
 8. Theapparatus of claim 2, wherein the system diagnostic module is structuredto determine that the SCR inlet and outlet NOx sensors are in theoperational state based on the correlation coefficient diagnosticfeature being greater than or equal to an operational correlationcoefficient diagnostic feature threshold and the gain diagnostic featurebeing within a set of operational gain diagnostic feature parameters. 9.The apparatus of claim 8, wherein the operational correlationcoefficient diagnostic feature threshold is 0.98 and the set ofoperational gain diagnostic feature parameters is 0.90 to 1.10.
 10. Amethod, comprising: adjusting at least one of an ignition timing and anengine speed for an engine to adjust an engine out nitrogen oxide (NOx)amount; interpreting measured SCR inlet NOx data from a SCR inlet NOxsensor and measured SCR outlet NOx data from a SCR outlet NOx sensor;determining a phase shift between the measured SCR inlet and SCR outletNOx data; applying the determined phase shift to the SCR outlet NOxdata; and determining a diagnostic feature based on the SCR inlet NOxdata and the phase shifted SCR outlet NOx data regarding a state of theSCR inlet and outlet NOx sensors.
 11. The method of claim 10, whereinthe diagnostic feature includes a first diagnostic feature and a seconddiagnostic feature, wherein the first diagnostic feature is a gaindiagnostic feature and the second diagnostic feature is a correlationcoefficient diagnostic feature.
 12. The method of claim 11, furthercomprising determining that the SCR inlet and outlet NOx sensors are inan operational state based on the gain diagnostic feature being within aset of operational gain diagnostic feature parameters and thecorrelation coefficient diagnostic feature being greater than or equalto an operational correlation coefficient diagnostic threshold.
 13. Themethod of claim 11, further comprising determining a reductant depositis present in the SCR system based on the gain diagnostic feature beingless than an inconclusive gain diagnostic feature parameter and thecorrelation coefficient diagnostic feature being within a set ofinconclusive correlation coefficient diagnostic feature parameters. 14.The method of claim 10, wherein the phase shift represents a durationfor an amount of exhaust gas to travel from the SCR inlet NOx sensor tothe SCR outlet NOx sensor.
 15. A system, comprising: an engine; anexhaust aftertreatment system in exhaust gas receiving communicationwith the engine, wherein the exhaust aftertreatment system includes aselective catalytic reduction (SCR) system; and a controllercommunicably coupled to the engine and the exhaust aftertreatmentsystem, the controller structured to: adjust a nitrogen oxide (NOx)amount out of the engine that is then received by the SCR system;interpret measured SCR inlet NOx data from a SCR inlet NOx sensor andmeasured SCR outlet NOx data from a SCR outlet NOx sensor; determine aphase shift between the measured SCR inlet and SCR outlet NOx data;apply the determined phase shift to the SCR outlet NOx data; anddetermine a diagnostic feature based on the SCR inlet NOx data and thephase shifted SCR outlet NOx data regarding a state of the SCR inlet andoutlet NOx sensors.
 16. The system of claim 15, wherein the phase shiftrepresents a duration for an amount of exhaust gas to travel from theSCR inlet NOx sensor to the SCR outlet NOx sensor.
 17. The system ofclaim 15, wherein the diagnostic feature includes a first diagnosticfeature and a second diagnostic feature, wherein the first diagnosticfeature is a gain diagnostic feature and the second diagnostic featureis a correlation coefficient diagnostic feature.
 18. The system of claim17, wherein the gain diagnostic feature includes a slope of a best fitline for the phase shifted SCR outlet NOx data and the SCR inlet NOxdata.
 19. The system of claim 18, wherein the correlation coefficientdiagnostic feature provides an indication of a linear relationship forthe SCR inlet NOx data and the phase shifted SCR outlet NOx data. 20.The system of claim 19, wherein the system diagnostic module isstructured to determine that the SCR inlet and outlet NOx sensors are inan operational state based on the gain diagnostic feature being within aset of operational gain diagnostic feature parameters and thecorrelation diagnostic feature being greater than or equal to anoperational correlation coefficient diagnostic feature threshold.